Russia has detained 25 Ukrainians suspected of plotting terrorist attacks on its territory during last month's Crimean referendum.
The Federal Security Service (FSB) said the detained members belong to the ultra-nationalist movements and were preparing attacks inside Russia.
The Ukrainians have been accused of taking photographs of Russian troop movements and of trying to make contact with extremist elements in Russia, the BBC reports.
Earlier, Ukrainian officials accused Russia, claiming that more than 30 FSB agents had been involved in planning operations against anti-government protesters in Kiev earlier this year.
Ukrainian Security Service chief Valentyn Nalyvaychenko also said the FSB had sent 'tonnes' of explosives and weapons by plane to Ukraine.
